1. Technical Field
The invention relates to sensors. In particular, the invention relates to devices employed as angle sensors.
2. Description of Related Art
Angle sensors are employed in a wide variety of applications to determine and monitor angular orientation and motion. For example, angle sensors are commonly employed in control systems to monitor and control an orientation and/or motion of a particular element of the system. Applications that employ angle sensors range from spacecraft and satellite attitude/orientation control to orienting a substrate during manufacturing. As such, angle sensors and angle sensing are commonly found in devices and systems such as consumer electronics, automobiles, manufacturing equipment, navigation systems, and even communication systems (e.g., antenna position control).
In general, angle sensors and angle sensing may be divided into two categories: absolute angle sensors/sensing and relative angle sensors/sensing. Absolute angle sensors/sensing determine an absolute orientation (and often an absolute position) of an object. Examples of absolute angle or position sensors are inertial sensors that measure an acceleration of the object in an inertial reference frame. Relative angle sensors/sensing, on the other hand, determine a relative angle or orientation of the object relative to a reference object, angle or direction (e.g., reference angle). Optical angle sensors are often employed as relative angle sensors. Exemplary optical relative angle sensors typically employ laser interferometery and/or collimation of a reference optical signal.
Micro-electromechanical systems (MEMs) inertial position sensors have been demonstrated in angle sensing applications. Unfortunately, MEMs devices often can be prohibitively expensive to manufacture and deploy. Laser interferometery and collimated optical source-based angle sensing is similarly expensive and typically require stable (often extremely stable) operating conditions for accurate angle determination. Even very simple normal angle of incidence detectors based on corner reflectors can suffer from degradation and calibration drift over time due, in part, to changes in a surface condition of the reflectors due to environmental factors. Moreover, these technologies often present a problem during integration into an integrated circuit (IC) or during manufacturing when conventional fabrication technologies is desired.